Phenomenology of isosinglet Higgs bosons in extended electroweak models

The phenomenological consequences of enlarging the scalar sector by adding isosinglet Higgs bosons to the usual single doublet are examined especially in the context of extended electroweak theories [extra U(1)’s] with additional isosinglet quarks as suggested by superstring-motivated ${\mathrm{E}}_6$ models. We comment on the differences between enlarging the Higgs sector with isosinglet versus isodoublet representations.